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Above time is expected as directory has around 22481 files. "ls -al" retrieves more file attributes details than normal "ls" command.
As per strace analysis, it is not found that any system call which took more than 1 sec. Accumulation of all calls took 1m26s as you see. Compared other user's
directory[has around ~4000 mails], it was not found this much delay. It just took less than 2 sec. Test and details :

#cat /var/log/strace_op|awk '{print $NF}'|egrep -v 'msg|dat|new|bin|size|\?'|sed 's/<//'|sed 's/>//'|awk 'BEGIN {sum=0.0} {sum+=$NF} END {print sum}'
If you see too much penalty in terms of consumption of retrieve time then please engage NetApp to perf analysis. Download perf tool
and retrieve data from filers. Handover this data to Netapp to further analysis.